Lens control apparatus, optical apparatus and lens control method

ABSTRACT

The optical apparatus includes a focus signal generator generating a focus signal from a photoelectrical conversion signal of an optical image formed by an optical system including a first lens unit for zooming and a second lens unit for focusing, a memory storing data indicating a relationship between positions of the first and second lens units, the data being generated for each predetermined in-focus distance. The controller moves the second lens unit in infinite and close directions. The controller changes a movement amount of a center position of the movement of the second lens unit in the infinite and close directions according to at least one selected from information on an operation of the optical system, information on a state of the optical system, and information on a photoelectric conversion operation of the optical image.

BACKGROUND OF THE INVENTION

The present invention relates to lens control processing performed in anoptical apparatus such as a video camera.

It is often the case that an optical apparatus including an opticalsystem of an inner focus type has a function of moving, when moving alens unit for zooming, a lens unit for focusing based on electronic camtracking data stored in a memory in advance to correct image planevariation accompanying zooming. This function facilitates zooming whilean in-focus state is maintained.

FIG. 8 shows a configuration of a conventional lens system of the innerfocus type. In the drawing, reference numeral 901 denotes a fixed frontlens, reference numeral 902 denotes a magnification-varying lens (zoomlens) for zooming, reference numeral 903 denotes an aperture stop,reference numeral 904 denotes a fixed lens, and reference numeral 905denotes a focus lens for focusing and having a correcting function(compensating function) of the image plane variation accompanyingzooming. Reference numeral 906 denotes an image pickup surface.

In such a lens system of the inner focus type, even though the lenssystem has a same focal length, different object distances change anin-focus position of the focus lens 905 for focusing on an object thatis a focusing target. When the object distance is changed at each focuslength, continuously plotting the in-focus positions of the focus lens905 at which in-focus object images are formed on the image pickupsurface 906 provides plural electronic cam tracks for the respectiveobject distances as shown in FIG. 9.

During zooming performed by moving the zoom lens 902, moving the focuslens 905 so as to trace a cam track selected from the plural electroniccam tracks according to the object distance enables zooming whilemaintaining an in-focus state.

As shown in FIG. 9, when the zoom lens 902 is moved from a telephotoside to a wide-angle side, the plural cam tracks come closer to eachother (converge) from a state where spaces therebetween have a certainwidth. Hence, it is easy to select one cam track according to the objectdistance. However, when the zoom lens 902 is moved from the wide-angleside to the telephoto side, it is difficult to accurately select one camtrack to be traced by the focus lens from the plural cam tracks havingnarrow spaces therebetween.

Japanese Patent No. 2901116 discloses an optical apparatus using a TV-AFmethod which determines a cam track to be traced by a focus lens usingan AF evaluation value during zooming. This apparatus compares, duringzooming, the AF evaluation values (focus signals) obtained by minutelymoving the focus lens in a close direction and an infinite directionwith each other to determine a direction in which an in-focus positionexists (hereinafter referred to as “in-focus direction”). Then, theapparatus moves a center position of the minute movement of the focuslens by a predetermined amount in the determined in-focus direction torepeat the minute movement, thereby determining one cam track to betraced by the focus lens during zooming.

However, as shown in FIG. 9, the spaces between the cam tracks becomewider as the zoom lens approaches the telephoto side. Thus, theapparatus disclosed in Japanese Patent No. 2901116 which determines thein-focus direction by using the AF evaluation values while minutelymoving the focus lens has a difficulty of determining the cam track tobe traced by the focus lens within a limited zooming time period.

Further, a large movement amount of the focus lens to obtain the AFevaluation values for the plural cam tracks may greatly exceed a depthof focus, which causes defocusing.

Moreover, in the TV-AF method, a cycle of obtaining the AF evaluationvalue corresponds to a cycle of a vertical synchronizing signal, andhence accuracy of determining the cam track decreases as a zooming speedbecomes higher. As a result, a frequency of erroneously determining thecam track increases.

Under these circumstances, Japanese Patent No. 2795439 discloses anoptical apparatus capable of maintaining an in-focus state even duringhigh-speed zooming and performing zooming without any dependence on ancaptured scene or camera work. This apparatus detects a distance (objectdistance) to a focusing target object, and restricts a movable range ofa focus lens for correcting a cam track (that is, for obtaining an AFevaluation value) based on the detected distance.

However, Japanese Patent No. 2795439 does not describe how a cam trackto be traced should be corrected within the restricted movable range ofthe focus lens. Hence, a simple restriction on the movable range of thefocus lens causes the following problems in a real image pickupenvironment.

First, the apparatus disclosed in Japanese Patent No. 2795439 restrictsthe movable range of the focus lens based on a distance detection resultand its detection accuracy. Then, the apparatus determines one cam trackto be traced from cam tracks within the movable range. However, as shownin FIG. 2, the movable range becomes wider toward the telephoto side. Asa result, in a case where the cam track to be traced by the focus lensis determined by repeating the minute movement of the focus lens in theinfinite and close directions around one cam track, zooming may befinished without determining the cam track.

As described above, in the TV-AF method, the cycle of obtaining the AFevaluation values corresponds to the cycle of the vertical synchronizingsignal, and hence the number of times of obtaining the AF evaluationvalues is reduced as the zooming speed increases. As a result, thenumber of times of moving the center position of the minute movement isreduced. In other words, since the cam track to be traced by the focuslens is determined within the movable range with a small number of timesof moving the center position of the movement, erroneous determinationof the cam track may often be made, which reduces determination accuracyof the cam track.

Similarly, during a long time exposure such as a so-called slow shutter,even if the zooming speed is not high, the cycle of obtaining the AFevaluation value corresponds to an exposure cycle. As a result, thedetermination accuracy of the cam track is reduced.

Thus, the optical apparatus disclosed in Japanese Patent No. 2795439does not determine the cam track to be traced by the focus lens fromplural cam tracks for all object distances from an infinite end to aclosest end, but narrows down the cam track to be traced within therestricted movable range based on the detection distances. However, whenhigh-speed zooming is performed, a number of and an amount of the centerposition movement need to be set by taking the number of times ofobtaining the AF evaluation value into consideration. Nonetheless,Japanese Patent No. 2795439 discloses no setting method that takes thenumber of times of obtaining the AF evaluation value into consideration

SUMMARY OF THE INVENTION

The present invention is directed to a lens control apparatus, anoptical apparatus and a lens control method enabling high qualityzooming while maintaining an in-focus state even during high-speedzooming.

The present invention provides as one aspect thereof a lens controlapparatus configured to move a first lens unit for zooming and a secondlens unit for focusing. The apparatus includes a focus signal generatorconfigured to generate a focus signal indicating a focus state of anoptical system from a photoelectrical conversion signal of an opticalimage formed by the optical system including the first and second lensunits, a memory configured to store data generated for eachpredetermined in-focus distance and indicating a relationship between aposition of the first lens unit and a position of the second lens unit,a controller configured to control, based on the data, movement of thesecond lens unit accompanying movement of the first lens unit, and adetector configured to detect information corresponding to a distance toa focusing target object. The controller moves the second lens unit inan infinite direction and a close direction within a movable range setbased on the information corresponding to the distance. The controllerchanges a movement amount of a center position of the movement of thesecond lens unit in the infinite and close directions according to atleast one selected from (a) information on an operation of the opticalsystem, (b) information on a state of the optical system, and (c)information on a photoelectric conversion operation of the opticalimage.

The present invention provides as another aspect thereof an opticalapparatus including an optical system configured to include a first lensunit for zooming and a second lens unit for focusing, and the above lenscontrol apparatus.

The present invention provides as still another aspect thereof a lenscontrol method for moving a first lens unit for zooming and a secondlens unit for focusing. The method includes a focus signal generationstep of generating a focus signal indicating a focus state of an opticalsystem from a photoelectrical conversion signal of an optical imageformed by the optical system including the first and second lens units,a control step of controlling movement of the second lens unitaccompanying movement of the first lens unit based on data generated foreach predetermined in-focus distance and indicating a relationshipbetween a position of the first lens unit and a position of the secondlens unit, and a detection step of detecting information correspondingto a distance to a focusing target object. The control step moves thesecond lens unit in an infinite direction and a close direction within amovable range set based on the information corresponding to thedistance. The control step changes a movement amount of a centerposition of the movement of the second lens unit in the infinite andclose directions according to at least one selected from (a) informationon an operation of the optical system, (b) information on a state of theoptical system, and (c) information on a photoelectric conversionoperation of the optical image.

Other aspects of the present invention will become apparent from thefollowing description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a video camera thatis an embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a correction range in acorrection operation of a cam track according to the embodiment.

FIG. 3 is a flowchart showing an operation in the video camera accordingto the embodiment.

FIGS. 4 to 7 are flowcharts showing a presupposed technology of thepresent invention.

FIG. 8 is a schematic diagram showing a configuration of a conventionalimage taking optical system.

FIG. 9 is a conceptual diagram showing in-focus cam tracks correspondingto object distances.

FIG. 10 shows in-focus cam tracks.

FIG. 11 shows a method of interpolation in a zoom lens moving direction.

FIG. 12 shows an example of a data table of in-focus cam tracks.

FIG. 13 shows a triangulation method.

FIG. 14 shows a ranging method using a phase difference detectionmethod.

FIG. 15 shows a relationship between AF evaluation values and in-focuspositions.

FIG. 16 shows fluctuation components of the AF evaluation values.

FIGS. 17A and 17B show minute movement of a focus lens and changes in AFevaluation value in the embodiment.

FIGS. 18A and 18B show movement of a center position of the minutemovement of the focus lens and changes in AF evaluation value in theembodiment.

FIGS. 19A and 19B show the minute movement of the focus lens and themovement of the center position in the embodiment.

FIG. 20 shows a relationship between a correction range and a depth offocus in the embodiment.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will hereinafter bedescribed with reference to the accompanying drawings.

(Presupposed Technology)

First, a basic technology for an embodiment of the present inventionwill be described before description of the embodiment.

FIG. 10 shows an example of a cam track tracking method of a focus lensin a lens system of an inner focus type.

In FIG. 10, reference characters Z₀, Z₁, Z₂, . . . , Z₆ denote positionsof a zoom lens. Reference characters a₀, a₁, a₂, . . . , a₆ and b₀, b₁,b₂, . . . , b₆ denote positions of the focus lens stored in advance in amicrocomputer (not shown) corresponding to object distances. Sets ofthese focus lens positions (a₀, a₁, a₂, . . . , a₆ and b₀, b₁, b₂, . . ., b₆) form in-focus cam tracks (hereinafter referred to as“representative cam tracks”) to be traced by the focus lens forrepresentative object distances.

Additionally, reference characters p₂, . . . , p₆ denote positions on anin-focus cam track to be traced by the focus lens calculated based onthe two representative cam tracks. The positions on the in-focus camtrack are calculated by the following expression (1):

p _((n+1)) =|p _((n)) −a _((n)) |/|b _((n)) −a _((n)) |×|b _((n+1)) −a_((n+1)) |+a _((n+1))   (1)

According to this expression (1), for example, when the focus lens islocated at the position p₀ in FIG. 10, an internal division ratio ofinternally dividing a line segment b₀−a₀ by p₀ is obtained, and a pointof internally dividing a line segment b₁−a₁ according to this internaldivision ratio is defined as p₁. A moving speed of the focus lens tomaintain an in-focus state can be known from a positional differencebetween p₁ and p₀ and a time period necessary for moving the zoom lensfrom Z₀ to Z₁.

Next, description will be made of a case where there is not arestriction in which a stop position of the zoom lens should be set onlyon a boundary of zoom areas having stored representative cam track data.FIG. 11 shows a method of interpolation in a moving direction of thezoom lens, where a part of FIG. 10 is extracted and a position of thezoom lens is optional.

In FIG. 11, a vertical axis indicates positions of the focus lens(hereinafter referred to as “focus lens positions”), and a horizontalaxis indicates positions of the zoom lens (hereinafter referred to as“zoom lens positions”). When the zoom lens positions are denoted by Z₀,Z₁, . . . , Z_(k−1), Z_(k), . . . , Z_(n), the focus lens positions aredenoted as follows for respective object distances:

a₀, a₁, . . . , a_(k−1), a_(k), . . . , a_(n)

b₀, b₁, . . . , b_(k−1), b_(k), . . . , b_(n)

When a zoom lens position is Z_(x) which is not located on the boundaryof the zoom areas (hereinafter referred to as “zoom area boundary”) anda focus lens position is p_(x), a_(x) and b_(x) are calculated by thefollowing expressions (2) and (3):

a _(x) =a _(k)−(Z _(k) −Z _(x))×(a _(k) −a _(k−1))/(Z _(k) −Z _(k−1))  (2)

b _(x) =b _(k)−(Z _(k) −Z _(x))×(b _(k) −b _(k−1))/(Z _(k) −Z _(k−1))  (3)

In other words, an internal division ratio is obtained from a currentzoom lens position and two zoom area boundary positions (e.g., Z_(k) andZ_(k−1) in FIG. 11). Then, two cam track data for a same object distancein the stored four representative cam track data (a_(k), a_(k−1), b_(k)and b_(k−1) in FIG. 11) are internally divided based on the aboveinternal division ratio to obtain a_(x) and b_(x).

Further, according to an internal division ratio obtained from a_(x),p_(x) and b_(x), two cam track data for a same focal length in thestored four representative cam track data are internally divided as inthe case of the expression (1). This way, p_(k) and p_(k−1) can beobtained.

During zooming from a wide-angle side to a telephoto side, a movingspeed of the focus lens necessary for maintaining an in-focus state canbe known from a difference between a focus position p_(k) which is atracking movement destination and a current focus position p_(x) and atime period necessary for moving the zoom lens from Z_(x) to Z_(k).

During zooming from the telephoto side to the wide-angle side, a movingspeed of the focus lens for maintaining an in-focus state can be knownfrom a difference between a focus position p_(k−1) which is a trackingmovement destination and the current focus position p_(x) and a timeperiod necessary for moving the zoom lens from Z_(x) to Z_(k−1).

FIG. 12 shows an example of table data of in-focus cam track informationstored in advance in the microcomputer. FIG. 12 shows focus lensposition data A_((n, v)) for respective object distances, the focus lensposition data being changed depending on zoom lens positions. The objectdistance changes in a column direction of a variable n, and the zoomlens position (focal length) changes in a row direction of a variable v.In this case, n=0 indicates an infinite object distance, the objectdistance changes to a closest distance side as n increases, and n=mindicates an object distance of 1 cm.

In FIG. 12, v=0 indicates a wide-angle end. As v becomes larger, thefocal length increases, and v=s indicates a zoom lens position of atelephoto end. Thus, table data of one column corresponds to onerepresentative cam track.

Next, description will be made of a cam track tracing method for solvingthe aforementioned problem in which the cam track to be traced by thefocus lens during zooming from the wide-angle side to the telephoto sidecannot be determined.

FIG. 15 shows change of an AF evaluation signal when the focus lens ismoved from a close side to an infinite side. The AF evaluation signalindicates a level of a high frequency component (sharpness signal) of animage pickup signal. A point P where the value of the AF evaluationsignal (hereinafter referred to “AF evaluation value”) becomes a peakcorresponds to an in-focus position of the focus lens.

Thus, continuously maintaining the focus lens at the peak (point P) ofthe AF evaluation value can solve the problem in which a cam track to betraced during zooming cannot be determined. However, the peak of the AFevaluation value is a relative value, which is sequentially changed dueto change of an angle of view or a contrast change of an object by thezooming. Thus, minutely moving the focus lens in the infinite directionand the close direction to observe changes in AF evaluation valueenables detection of a direction in which the peak (in-focus position)of the AF evaluation value is present.

In FIG. 15, when the focus lens is minutely moved with a point A or apoint B set as a center position, the AF evaluation value repeatedlyincreases and decreases, exhibiting great fluctuation. A peak of the AFevaluation value is present in a direction in which the AF evaluationvalue increases during the minute movement, and hence moving the focuslens in that increase direction enables specifying of the peak of the AFevaluation value.

At the point P, when the focus lens is minutely moved, the AF evaluationvalue fluctuates in a small width. This fluctuation is as shown in FIG.16. In the vicinity of an in-focus point, even when the focus lens ismoved in the infinite and close directions, AF evaluation values tend todecrease in both those directions, and hence the in-focus point isspecified by using this characteristic. When the AF evaluation valuesare repeatedly obtained by continuous reciprocation of the focus lens ina same area plural number of times, a determination is made that thefocus lens is located at an in-focus point.

In FIG. 17A, a cam track (set of focus lens positions) to be traced bythe focus lens during zooming performed while maintaining an in-focusstate for an object located at a certain distance is denoted byreference numeral 1900. Minute movement of the focus lens will bedescribed in which the cam track 1900 is a center cam trackcorresponding to a center position of the minute movement of the focuslens.

When the focus lens is located at a point F₀ away by L from the centercam track to the infinite side, in order to obtain an AF evaluationvalue at the point F₀, the focus lens is moved to a point F₁ (point awayby L from the center cam track to the infinite side) with the sameinclination as that of the center cam track 1900. Thus, an AF evaluationvalue E₀ is obtained.

Then, the focus lens is moved to a point F₂ away by L from the centercam track 1900 to the close side.

Then, in order to obtain an AF evaluation value at the point F₂, thefocus lens is moved to a point F₃ (point away by L from the center camtrack 1900 to the close side) with the same inclination as that of thecenter cam track 1900, and thereby an AF evaluation value E₂ isobtained. Similarly, the focus lens is moved to a point F₄ away by Lfrom the center cam track 1900 to the infinite side. Repeating theseoperations enables minute movement of the focus lens around the centercam track 1900.

In the above movement of the focus lens, since the cam track to betraced (in-focus cam track) is the center cam track 1900, the AFevaluation values E₀, E₂, E₄, . . . of the close side and the infiniteside obtained by the minute movement are approximately constant as shownin FIG. 17B. In other words, the lens system is in a situation wherezooming is performed while maintaining an in-focus state.

However, the center cam track is not always a cam track (in-focus camtrack) to be traced by the focus lens. Referring to FIG. 18A, this casewill be described. First, when the focus lens is located at a point F′₀,the minute movement is performed with a virtual center cam track 1901set as a center. When the focus lens is moved from the point F′₀ to apoint F′₅, AF evaluation values E′₀, E′₂, and E′₄ on the track arestored. These AF evaluation values are compared with one another todetermine a next focus position F′₅.

When the AF evaluation values are as shown in FIG. 18B, fromrelationships of E′₀<E′₂ and E′₄<E′₂, it can be known that a peak of theAF evaluation value is present in a direction of E′₂, in other words,there is a cam track to be traced (in-focus cam track) on the closeside.

Thus, the position F′₅ is moved closer by an amount W to the close sidethan the virtual center cam track 1901. Then, the minute movement isperformed again with a cam track (virtual center cam track) 1902 locatedcloser by the amount W to the close side than the cam track 1901.

Similarly, with the virtual center cam track 1902 set as a center, theminute movement is performed several number of times to compare obtainedAF evaluation values with one another. The amount (center movementamount) W is set based on the comparison result, and change of thecenter cam track is repeatedly performed until an in-focus cam track isdetermined.

As described above, this embodiment determines (specifies), based on theAF evaluation values obtained in the minute movement of the focus lensduring zooming, a cam track according to which the AF evaluation valuesare approximately constant while changing the center cam track. As aresult, the problem in which the cam track to be traced by the focuslens during zooming from the wide-angle side to the telephoto sidecannot be determined can be solved.

The aforementioned zooming control is generally performed, for a reasonthat focus detection is performed by using an image pickup signal fromthe image pickup element, in synchronization with a verticalsynchronizing signal of an image (video).

FIG. 7 is a flowchart showing the zooming control performed in themicrocomputer. When processing of the zooming control is started at StepS701, the microcomputer performs at Step S702 initial settings. In theinitial settings, a RAM and various ports in the microcomputer areinitialized.

At Step S703, the microcomputer detects a state of an operation systemof a camera body. The microcomputer receives information on a zoomswitch unit operated by a user, and displays magnification variation(zooming) operation information such as a zoom lens position on thedisplay in order to notify the user of zooming execution.

At Step S704, the microcomputer performs AF processing. In other words,the microcomputer performs autofocus processing according to changes ofthe AF evaluation signal.

At Step S705, the microcomputer performs zooming processing. In otherwords, the microcomputer performs processing of a compensating operationfor maintaining an in-focus state during zooming. Specifically, in orderto trace the cam track shown in FIG. 9, the microcomputer calculates astandard moving direction and a standard moving speed of the focus lens.

At Step S706, the microcomputer selects any of the moving directions andthe moving speeds for the zoom lens and the focus lens calculated fromthe processing at Steps S704 and S705 to use during the AF processingand the zooming. This process is for moving the zoom lens and the focuslens between a controlled telephoto end and a controlled wide-angle endand a controlled closest end and a controlled infinite end, eachcontrolled end being provided by software such that the lens comes intocontact with mechanical ends.

At Step S707, the microcomputer outputs a control signal to a motordriver according to information of the moving direction and informationof the moving speed for zooming and focusing set at Step S706 to controldrive and stop of each lens. After completion of the processing at StepS707, the microcomputer returns to step S703.

The series of processing shown in FIG. 7 is executed in synchronizationwith the vertical synchronizing signal (that is, the microcomputerstands by until input of a next vertical synchronizing signal duringprocessing at Step S703).

FIGS. 5 and 6 show a control flow performed once by the microcomputerduring one vertical synchronization time period, showing in detail theprocessing performed at Step S705 shown in FIG. 7.

Hereinafter, referring to FIGS. 4 to 7 and 10, the processing will bedescribed.

At Step S400 shown in FIG. 4, the microcomputer sets a driving speed(zooming speed Zsp) of a zoom motor to enable a natural zoomingoperation according to operation information of the zoom switch unit.

At Step S401, the microcomputer compares the AF evaluation values of theclose side and the infinite side with respect to the center cam trackobtained by the minute movement with one another to determine adirection of a center movement. In this determination method, as shownin FIG. 17B, at least three continuous AF evaluation values such asinfinite side AF evaluation values E₀ and E₄ and close side AFevaluation values E₂ and E₆ are compared with one another to set adirection of a higher AF evaluation value as a center movementdirection.

When the focus lens is continuously reciprocated a predetermined numberof times in a same area with respect to the center cam track torepeatedly obtain AF evaluation values, the microcomputer determinesthat this area including an in-focus point (in-focus cam track). Whenperforming the center movement, the microcomputer sets signs + and −respectively indicating the close side and the infinite side.

Subsequently, at Step S402, the microcomputer determines a necessity ofthe center movement. If the center movement is necessary (that is, ifthe lens system is in an out-of-focus state where no AF evaluation valueindicating an in-focus state is obtained), the microcomputer calculatesat step S403 the center movement amount W. If no center movement isnecessary, in other words, if the lens system is in an in-focus state,the microcomputer returns to step S405.

The center movement amount W is calculated at Step S403 based on a focallength (zoom lens position) and the like. As shown in FIG. 9, a spacebetween the cam tracks varies depending on the focal length. The camtracks are collected so as to be converged on the wide-angle side, whilethe spaces therebetween are gradually increased toward the telephotoside. For example, when the center movement amount W is set to beconstant irrespective of the focal length, the cam tracks are denselyset on the wide-angle side, and hence one center movement enableschanging between cam tracks for different object distances.

On the other hand, since the spaces between the cam tracks are wider onthe telephoto side than those on the wide-angle side, if the centermovement amount W is equal to that on the wide-angle side, changingbetween cam tracks for different object distances is difficult. Thus,the center movement amount W is changed depending on the focal length,and its value is determined based on the space between the cam tracks.The center movement amount W is set to a value enough for the focus lensto minutely move (cover) on all the cam tracks from a cam track for aninfinite object distance to a cam track for a closest object distance.

A sign is added to the determined center movement amount W based on themoving direction of the focus lens. At Step S404, the microcomputer addsthe center movement amount W to a minute movement center focus lensposition P_(x) to update P_(x) as follows:

P _(x) =P _(x) ±W

When the center movement occurs, the focus lens is minutely moved byusing this updated P_(x) as a new minute movement center focus lensposition.

Next, at Step S405, the microcomputer performs processing shown in FIG.5 by using three cam track parameters α, β and γ to detect one of thecam tracks shown in FIG. 9 on which the zoom lens and the minutemovement center focus lens position are currently located. Hereinafter,the processing of FIG. 5 will be described by assuming that an in-focusstate is maintained on current lens positions.

At Step S501 shown in FIG. 5, the microcomputer calculates a zoom area vwhere a current zoom position Z_(x) is located in a data table shown inFIG. 12. The zoom area v is one of zoom areas formed by equally dividingan entire zoom range from the wide-angle end to the telephoto end into sareas. Referring to FIG. 6, this calculation method will be described.

At Step S601, the microcomputer clears a zoom area variable v. At StepS602, the microcomputer calculates a zoom lens position Z_((v)) on aboundary of the zoom area v with the following expression (6). This zoomlens position Z_((v)) corresponds to the zoom lens positions Z₀, Z₁, Z₂,. . . shown in FIG. 10.

Z_((v))=(telephoto end zoom lens position−wide-angle end zoom lensposition)×v/s+wide-angle end zoom lens position   (6)

At Step S603, the microcomputer determines whether or not the zoom lensposition Z_((v)) obtained at Step S602 is coincident with the currentzoom lens position Z_(x). If the zoom lens position Z_((v)) iscoincident with the current zoom lens position Z_(x), the microcomputerat step S607 sets a boundary flag to 1 which indicates that the zoomlens position Z_(x) is located on the boundary of the zoom area v.

If the zoom lens position Z_((v)) is not coincident with the currentzoom lens position Z_(x) at Step S603, the microcomputer at Step S604determines whether or not a relationship of Z_(x)<Z_((v)) isestablished. If the relationship is established at Step S604, thecurrent zoom lens position Z_(x) is located between Z_((v−1)) andZ_((v)), and the microcomputer at Step S606 sets the boundary flag to 0.If the relationship is not established at Step S604, the microcomputerat step S605 increments the zoom area v and then returns to step S602.

Repeating the above processing enables, when the processing goes out ofthe flowchart of FIG. 6, detection of whether the current zoom positionZ_(x) is located in the v-th (=k-th) zoom area in the data table of FIG.12 and further located on the zoom area boundary.

Returning to FIG. 5, at Step S501, the current zoom area has beendetermined by the processing of FIG. 6. Hence, in the followingprocessing, the microcomputer calculates a position of the focus lens inthe data table of FIG. 12.

First, at Step S502, the microcomputer clears an object distancevariable n. At Step S503, the microcomputer determines whether or notthe current zoom lens position is located on the zoom area boundary. Ifthe boundary flag is 0, the microcomputer proceeds to Step S505 andsubsequent steps since the current zoom lens position is not located onthe zoom area boundary.

At Step S505, the microcomputer sets Z_((v)) to Z_(k), and sets Z_((v−1)) to Z_(k−1). Then, at Step S506, the microcomputer reads fourtable data A_((n, v−1)), A_((n, v)), A_((n+1, v−1)) and A_((n+1, v)). AtStep S507, the microcomputer calculates a_(x) and b_(x) with theexpressions (2) and (3).

On the other hand, if the boundary flag is 1 at Step S503, themicrocomputer at Step S504 loads an in-focus position A_((n, v))corresponding to a zoom lens position (v in this description) at theobject distance n and A_((n+1, v)) corresponding to a zoom lens positionat the object distance n+1. The microcomputer respectively stores themas a_(x) and b_(x) in the memory.

At Step S508, the microcomputer determines whether or not the minutemovement center focus lens position P_(x) is equal to or higher thana_(x). If P_(x) is equal to or higher than a_(x), the microcomputer atstep S509 determines whether or not the minute movement center focuslens position P_(x) is equal to or higher than b_(x). If P_(x) is notequal to or higher than b_(x), the minute movement center focus lensposition P_(x) is located between the object distances n and n+1, andthe microcomputer stores cam track parameters for this case in thememory at Steps S513 to S515. At step S513, the microcomputer setsα=P_(x)−a_(x). At Step S514, the microcomputer sets β=b_(x)−a_(x). AtStep S515, the microcomputer sets γ=n.

The microcomputer determines “No” at Step S508 when the minute movementcenter focus lens position P_(x) is a superinfinite position. In thiscase, the microcomputer at Step S512 sets α=0, and then proceeds to StepS514 and subsequent steps thereof to store cam track parameters for theinfinite object distance in the memory.

The microcomputer determines “Yes” at Step S509 when the minute movementcenter focus lens position P_(x) is located further to the close side.In this case, the microcomputer increments the object distance n at StepS510, and determines whether or not the object distance n is further tothe infinite side than a position m corresponding to the closestposition at Step S511. If the position n is further to the infinite sidethan the closest distance position m, the microcomputer returns to StepS503.

The microcomputer determines “No” at Step S511 when the minute movementcenter focus lens position P_(x) is located at a superclose position. Inthis case, the microcomputer proceeds to Step S512 and subsequent stepsthereof to store cam track parameters for the closest object distance inthe memory.

Referring back to FIG. 4, as described above, at Step S405, themicrocomputer stores the cam track parameters for detecting whether thecurrent zoom lens position and the minute movement center focus lensposition are located on the cam tracks shown in FIG. 9.

Then, at Step S406, the microcomputer calculates a zoom lens position(movement destination position from the current zoom lens position)Z′_(x) where the zoom lens will reach after one vertical synchronizingtime period (1V). The zoom lens position Z′_(x) after one verticalsynchronizing time period can be calculated by the following expression(7), where Zsp(pps) denotes a zooming speed determined at Step S400.

Z′ _(x) =Z _(x) ±Zsp/vertical synchronizing frequency   (7)

In this expression, pps represents a unit for a rotation speed of astepping motor used as the zoom motor, specifically a step amount (1step=1 pulse) of rotation per second. Signs + and − of the expression(7) respectively indicate a telephoto direction and a wide-angledirection corresponding to the moving direction of the zoom lens.

Then, at Step S407, the microcomputer determines a zoom area v′ wherethe zoom lens position Z′_(x) is located. At Step S407, themicrocomputer performs processing similar to that shown in FIG. 6,specifically processing where Z_(x) and v in FIG. 6 are respectivelyreplaced by Z′_(x) and v′.

At step S408, the microcomputer determines whether or not the zoom lensposition Z′_(x) after one vertical synchronizing time period is locatedon the boundary of the zoom area. In the case of the boundary flag=0,the microcomputer determines that the zoom lens position Z′_(x) is notlocated on the boundary, and then proceeds to Step S409 and subsequentsteps thereof.

At Step S409, the microcomputer sets Z_(x)←Z_((v′)),Z_(k−1)←Z_((v′, −1)). At Step S410, the microcomputer reads four tabledata A_((γ, v′−1)), A_((γ, v′)), A_((γ+1, v′)) and A_((γ+1, v′)) wherean object distance γ is specified by processing of FIG. 5. At Step S411,the microcomputer calculate a′_(x) and b′_(x) by the expressions (2) and(3).

On the other hand, if the microcomputer determines “Yes” at Step S408,the microcomputer at Step S412 loads an in-focus position A_((γ, v′))corresponding to the zoom area v′ at the object distance γ and anin-focus position A_((γ+1, v′)) corresponding to the zoom area v′ at theobject distance γ+1. Then, the microcomputer stores these in-focuspositions as a′_(x) and b′_(x) in the memory.

Next at Step S413, the microcomputer calculates an in-focus position(target position) P′_(x) of the minute movement center focus lens whenthe zoom lens position reaches Z′_(x). By using the expression (1), atracking target position after one vertical synchronizing period of timecan be represented by the following expression (8):

P′ _(x)=(b′ _(x) −a′ _(x))×α/β+a′ _(x)   (8)

Next at Steps S414 to S417, the microcomputer performs signdetermination of an amplitude L based on a minute movement count N. Asshown in FIG. 17A, the minute movement is synchronized with the minutemovement count N. At Step S414, when the minute movement count N is oneof 0, 1, 4 and 5, the focus lens is moved further on the infinite sidethan the center cam track of the minute movement, and hence themicrocomputer subtracts the amplitude L from the minute movement centerfocus lens position. As a result, at Step S415, a focus lens positionP′_(L) ahead by 1V becomes P′_(x)−L.

Similarly, at Step S414, when the minute movement count N is one of 2,3, 6 and 7, the focus lens is moved further on the close side than theminute movement center cam track, the microcomputer adds the amplitude Lto the minute movement center focus lens position. Thus, at Step S416,the focus lens position P′_(L) ahead by 1V becomes P′_(x)+L. FIG. 19Ashows the minute movement of the focus lens from the infinite side tothe close side. The amplitude L is determined by a depth of focus or thelike.

Next at Step S417, the microcomputer increments the minute movementcount N. Then at Step S418, when the minute movement count N reaches 8,the microcomputer initializes the minute movement count N to 0. Amaximum value of the minute movement count N is not necessarily 8. Inthis embodiment, four minute movements in the infinite direction, theinfinite direction, the close direction and the close directionconstitute one cycle. However, one cycle may be constituted by alternatetwo movements in the infinite direction and the close direction.

The above processing enables calculation of the focus lens positionP′_(L) ahead by 1V. After the completion of this processing, at StepS706 of FIG. 7, the microcomputer selects moving directions and speedsof the focus lens and the zoom lens according to an operation mode.

As shown in FIG. 19B, in the case of a zooming operation with a centermovement amount W, a difference ΔF between a value of the focus lensposition P′_(L) ahead by 1V and the current focus lens position P_(L)(point away by L from the minute movement center position P_(x))obtained at Step S415 or S416 is represented as follows:

ΔF=P′ _(L) −P _(L)

ΔF={(b′ _(x) −a′ _(x))×α/β+a′ _(x) ±L}−(P _(x) ±L)±W

The sign of L is set based on the minute movement count N, and thecenter movement amount W is calculated based on a comparison result ofthe AF evaluation values.

Thus, depending on whether the difference AF is positive or negative, adirection for moving the focus lens is selected from one of the closedirection and the infinite direction. As a result, the minute movementof the focus lens enables determination of a cam track to be traced.

The presupposed technology of the present invention has been described.Hereinafter, differences of an embodiment of the present invention fromthe presupposed technology will be described.

Embodiment

FIG. 1 shows a configuration of a video camera as an image pickupapparatus (optical apparatus) including a lens control apparatus that isan embodiment of the present invention mounted thereon. This embodimentwill describe an example where the present invention is applied to alens-integrated image pickup apparatus. However, alternative embodimentsof the present invention include an interchangeable lens (opticaldevice) of an image pickup system including the interchangeable lens anda camera body to which the interchangeable lens is mounted.

In this case, a microcomputer in the interchangeable lens performs azoom operation described below in response to a signal transmitted fromthe camera body. The alternative embodiments of the present inventionfurther include not only the video camera but also various other imagepickup apparatuses such as a digital still camera.

In FIG. 1, in order from an object side (left in the figure), referencenumeral 101 denotes a front lens unit, and reference numeral 102 denotesa zoom lens unit (first lens unit, and hereinafter referred to as “zoomlens”) which is moved in an optical axis direction to perform zooming(variation of magnification). Reference numeral 103 denotes an aperturestop as a light amount adjuster, and reference numeral 104 denotes afixed lens unit. Reference numeral 105 denotes a focus lens unit (secondlens unit, hereinafter referred to as “focus lens”) which has a focusingfunction and a compensating function of correcting image plane variationdue to zooming.

The lens units 101, 102, 104 and 105 and the aperture stop 103constitute an image taking optical system. The image taking opticalsystem is a rear focus (inner focus) optical system including four lensunits having positive, negative, positive and positive optical powers inorder from the object side. In the figure, each lens unit includes onelens. In reality, however, each lens unit may include plural lenses.

Reference numeral 106 denotes an image pickup element such as a CCDsensor or a CMOS sensor. A light flux from an object passed through theimage taking optical system forms an image on the image pickup element106. The image pickup element 106 photoelectrically converts the objectimage to output an image pickup signal (photoelectric conversionsignal). The image pickup signal is amplified to an optimal level by anamplifier (AGC) 107 to be input to a camera signal processing circuit108.

The camera signal processing circuit 108 converts the input image pickupsignal into a standard television signal (video signal) to output thesignal to an amplifier 110. The television signal amplified to anoptimal level by the amplifier 110 is output to a magneticrecording/reproducing device 111 to be recorded in a magnetic recordingmedium such as a magnetic tape. As the recording medium, other mediasuch as a semiconductor memory and an optical disk may be used.

The television signal amplified by the amplifier 110 is transmitted toan LCD display circuit 114 to be displayed as a captured image by an LCD115. The LCD 115 also displays an image to notify a user of an imagepickup mode, an image pickup state and various warnings. Such an imageis generated by a character generator 113 controlled by a cameramicrocomputer 116, and is mixed to the television signal by the LCDdisplay circuit 114, thereby being superimposed on the captured imageand displayed therewith.

The image pickup signal input to the camera signal processing circuit108 can be simultaneously compressed by using an internal memory, andthen recorded in a still image recording medium 112 such as a cardmedium.

The image pickup signal input to the camera signal processing circuit108 is also input to an AF signal processing circuit 109 as a focussignal generator. An AF evaluation value signal (focus signal) generatedby the AF signal processing circuit 109 and indicating a focus state ofthe image taking optical system is read by communication with the cameramicrocomputer 116.

The camera microcomputer 116 reads states of a zoom switch 130 and an AFswitch 131, and detects a state of a photo switch 134.

In a state where the photo switch 134 is half-pressed, a focusingoperation by AF is started, and focus lock is activated in an in-focusstate. In a state where the photo switch 134 is fully pressed, the focuslock is performed irrespective of an in-focus or out-of focus state tocapture an image in a memory (not shown) of the camera signal processingcircuit 108, and a still image is recorded in a magnetic tape or thestill image recording medium 112.

The camera microcomputer 116 determines whether a current image pickupmode is a moving image pickup mode or a still image pickup modeaccording to a state of a mode switch 133, and controls the magneticrecording/reproducing device 111 and the still image recording medium112 via the camera signal processing circuit 108. The cameramicrocomputer 116 accordingly supplies a television signal suited torecording. When the mode switch 133 is set in a reproduction mode, thecamera microcomputer 116 controls reproduction of the television signalsrecorded in the magnetic recording/reproducing device 111 and the stillimage recording medium 112.

The camera microcomputer 116 includes a computer zoom unit 119 providedas a controller. When the zoom switch 130 is operated while the AFswitch 131 is OFF, the computer zoom unit 119 outputs a zoom signal to azoom motor driver 122 via a motor controller 118 according to aninternal program. The zoom signal is for moving the zoom lens 102 in atelephoto direction or a wide-angle direction corresponding to adirection where the zoom switch 130 is operated.

The zoom motor driver 122 moves the zoom lens 102 via a zoom motor 121in response to reception of the zoom signal in a direction correspondingto the operation direction of the zoom switch 130.

A cam data memory (memory) 120 stores representative cam track datashown in FIG. 11 or data of cam track parameters, which are created inadvance for each in-focus distance. The computer zoom unit 119 generatescam track data (cam track information) based on the stored data. Thecomputer zoom unit 119 drives a focus motor 125 via a focus motor driver126 based on the cam track data, and moves the focus lens 105 so as tocorrect the image plane variation accompanying zooming.

The camera microcomputer 116 includes an AF control unit 117.

When the AF switch 131 is ON and the zoom switch 130 is operated,zooming needs to be performed while maintaining an in-focus state. Inthis case, the computer zoom unit 119 obtains the AF evaluation valuesignal from the AF signal processing circuit 109 and distanceinformation to an object (focusing target object) from an objectdistance detection circuit (detector) 127. Then, the computer zoom unit119 moves the zoom lens 102 and the focus lens 105 based on the camtrack data, the AF evaluation value signal and the distance information.

A detection signal (information corresponding to distance) from theobject distance detection circuit 127 is subjected to calculationprocessing by a distance information processor 128 of the cameramicrocomputer 116, and is output as the distance information to thecomputer zoom unit 119.

When the zoom switch 130 is not operated while the AF switch 131 is ON,the AF control unit 117 outputs a signal to the focus motor driver 126via the motor controller 118 so as to move the focus lens 105 such thata level of the AF evaluation value signal becomes a maximum. Thus, thefocus lens 105 is moved via the focus motor 125 to perform an autofocusoperation.

The object distance detection circuit 127 measures a distance to theobject by a triangulation method using an active sensor, and outputs thedistance information which is a measuring result. In this case, as theactive sensor, an infrared sensor which is often used in a compactcamera can be used.

This embodiment describes an example where distance detection isperformed by the triangulation method. However, other distance detectionmethods can be employed. For example, a TTL phase difference detectionmethod can be employed in which a signal (phase difference signal asinformation corresponding to distance) corresponding to the objectdistance is obtained.

In this case, an element such as a half-prism or a half-mirror fordividing a light flux that has passed through an exit pupil of the imagetaking optical system is provided, and the light flux emerging from theelement is guided to at least two line sensors via a sub-mirror or animage-forming mirror. Then, correlation calculation is performed onoutputs of these line sensors, thereby obtaining a deviation directionand a deviation amount of the outputs. An object distance is obtainedfrom the deviation direction and amount.

FIGS. 13 and 14 show a principle of distance calculation performed bythe triangulation method or the phase difference detection method. InFIG. 13, reference numeral 201 denotes an object, reference numeral 202denotes an image-forming lens for a first optical path, and referencenumeral 203 denotes a line sensor for the first optical path. Referencenumeral 204 denotes an image-forming lens for a second optical path, andreference numeral 205 denotes a line sensor for the second optical path.The line sensors 203 and 205 are disposed away from each other by a baselength B.

Of light fluxes from the object 201, a light flux passing through thefirst optical path forms an image on the line sensor 203 by theimage-forming lens 202, and a light flux passing through the secondoptical path forms an image on the line sensor 205 by the image forminglens 204.

FIG. 14 shows an example of signals (object image signals) C and D readfrom the line sensors 203 and 205 received the two object images formedby the light fluxes passing through the first and second optical paths.

The two line sensors are separated from each other by the base length B.Hence, as obvious from FIG. 13, the object image signals C and D aredeviated from each other by the number of pixels X. Thus, a correlationbetween the two object image signals C and D is calculated by shiftingpixels, and a pixel shift amount to maximize the correlation isobtained, thereby enabling calculation of X. From this X, the baselength B, and a focal length f of each of the image forming lenses 202and 204, a distance L to the object can be obtained by L=B×f/X, which isthe principle of the triangulation method.

For the detector, a method of obtaining a signal equivalent to adistance to the object by measuring a propagation speed using anultrasonic sensor can be used.

The distance information from the object distance detection circuit 127is transmitted to the distance information processor 128. The distanceinformation processor 128 performs the following three processes PROCESS1 to PROCESS 3.

(PROCESS 1) The distance information processor 128 calculates, of thecam tracks for various object distances shown in FIG. 9, a cam track onwhich the zoom lens 102 and the focus lens 105 are currently located.The cam track can be calculated, for example, as described at Step S405of FIG. 4.

Specifically, the distance information processor 128 calculates anobject distance (meters) corresponding to a virtual cam track whichinternally divides a γ column cam track and a γ+1 column cam track at ainternal division ratio of α/β by using the current lens positions andthe cam track parameters a, β and γ. The cam track parameters α, β and γare converted into the object distance by using predeterminedcorrelation table data. Thus, a real distance to the object can beobtained.

(PROCESS 2) The distance information processor 128 performs reverseconversion of the distance to the object obtained from the objectdistance detection circuit 127 by using the correlation table datadescribed above in PROCESS 1 to obtain a cam track expressed by the camtrack parameters α, β and γ. In the reverse conversion, of thecorrelation table data, wide-angle side data where the cam tracks ofFIG. 9 are converged are not used, but telephoto side data where the camtracks are dispersed are used. Thus, high resolution cam trackparameters (cam tracks) can be obtained.

(PROCESS 3) A difference between the real distance to the objectobtained in PROCESS 1 and the distance to the object obtained from theobject distance detection circuit 127 in PROCESS 2, and a directionthereof are calculated.

Among these PROCESSES 1, 2 and 3, PROCESS 2 enables determination of acam track corresponding to the distance information detected by theobject distance detection circuit 127.

The camera microcomputer 116 also performs exposure control. The cameramicrocomputer 116 refers to a luminance level of the television signalgenerated by the camera signal processing circuit 108, and controls aniris driver 124 to drive an IG meter 123 so that the luminance level canbe appropriate for exposure. Thus, the camera microcomputer 116 controlsan aperture diameter (aperture amount or aperture value) of the aperturestop 103.

The aperture diameter of the aperture stop 103 is detected by an irisencoder 129 to perform feedback control of the aperture stop 103. Whenappropriate exposure control cannot be performed only by the aperturestop 103, an exposure time period of the image pickup element 106 iscontrolled by a timing generator (TG) 132 to perform a fast shutter anda slow shutter which is called as long-time exposure. When there is ashortage of exposure due to image pickup under low illuminance or thelike, the camera microcomputer 116 controls a gain of the televisionsignal via the amplifier 107.

The user can manually set an image pickup mode and a camera functionwhich are suited to each of various image pickup conditions.

Next, referring to FIG. 3, an algorithm during zooming will bedescribed. In this embodiment, the computer zoom unit 119 included inthe camera microcomputer 116 executes the aforementioned processing andthe following processing according to computer programs.

In this embodiment, based on the distance information obtained by theobject distance detection circuit 127, a cam track to be traced(followed) by the focus lens 105 is determined (generated), and therebyzooming is performed while maintaining an in-focus state.

FIG. 3 shows an example of a method for performing a zooming operationwhile determining (generating) a zoom tracking curve that is a cam trackto be followed by using the distance information. This method isespecially effective in a case where a cycle of sampling of the AFevaluation value signals is coarse during superfast zooming or the like,and therefore accuracy of determining the zoom tracking curve cannot besufficiently increased only by the AF evaluation value signals that arereference signals of TV-AF.

FIG. 3 shows the aforementioned processing performed at Step S705 ofFIG. 7 in this embodiment. Processing (step) similar to that of FIG. 4is denoted by a same reference numeral to omit its description. In FIG.3, portions where same circled numerals are added are connected to eachother.

At Step S400, the computer zoom unit 119 determines a moving speed(hereinafter referred to as “zooming speed”) of the zoom lens 102 duringzooming.

At Step S300, the computer zoom unit 119 calculates cam track parametersαd, βd and γd corresponding to the distance information obtained by theobject distance detection circuit 127, for example, by the followingmethod.

First, in order to obtain a correlation between the distance informationand the representative cam tracks shown in FIG. 9, table data of acorrelation between a change of the distance information and the camtrack parameters are created in a range where the cam tracks (camcurves) for the representative object distances have a uniform shape.The table data enables calculation of the cam track parameters byinputting the distance information. For an object distance where theshape of the cam track changes, a look-up table representing anothercorrelation is provided. Providing a plurality of such look-up tablesenables obtaining of the cam track parameters for all the objectdistances.

Concerning a focal length, of the cam track data shown in FIG. 9discretely stored in the memory, cam track parameters on a long focallength side where resolution of the cam track parameters α, β and γ ishighest are permitted to be output. This makes it possible to extract,according to the distance information, cam track parameters from atelephoto side point where the cam tracks are dispersed as shown in FIG.9, even when the current lens position is located in a wide-angle sidearea where the cam tracks are converged.

Accordingly, at a point of time when the zoom lens 102 is located on thewide-angle side, interpolation calculation is performed based on the camtrack parameters on the telephoto side, whereby one cam track to betraced by the focus lens 105 can be determined.

Step S300 is executed for each predetermined cycle (e.g., one verticalsynchronizing cycle). Thus, even when the object distance changes duringzooming, based on the distance information from the object distancedetection circuit 127, latest cam tracks to be traced by the focus lens105 are sequentially updated.

At Step S301, the computer zoom unit 119 determines a correction rangeof the cam tracks based on the cam track parameters αd, βd and γdcorresponding to the distance information obtained by the objectdistance detection circuit 127. This correction range corresponds to amovable range of the focus lens 105 during a correction operation of thecam tracks using the AF evaluation values, in other words, a movablerange for the minute movement of the focus lens 105 performed to obtainthe AF evaluation values, for example, a range between an upper limit201 and a lower limit 202 shown in FIG. 2.

In this embodiment, for example, when the distance information (objectdistance) 203 obtained by the object distance detection circuit 127 is 5m, the correction range is restricted within an increase/decrease rangeof ±50 cm with respect to the object distance. In other words, the upperlimit 201 is equivalent to a cam track corresponding to an objectdistance of 4.5 m, and the lower limit 202 is equivalent to a cam trackcorresponding to an object distance of 5.5 m. This increase/decreaserange may be determined according to detection accuracy of the objectdistance detection circuit 127.

In this embodiment, after a cam track to be followed (hereinafterreferred to as “following cam track”) is roughly determined based on thedistance information, the following cam track is redetermined(regenerated) more accurately by the minute movement of the focus lens105 performed to obtain the AF evaluation values. The correction rangeis set to restrict a movable range of the focus lens 105 during theminute movement.

Employing such a configuration eliminates necessity of setting detectionresolution (detection accuracy) of the object distance detection circuit127 so high, accordingly enabling realization of a low-cost and compactoptical apparatus.

Conventionally, an object distance has been undeterminable duringzooming from the wide-angle side to the telephoto side. As a result, acenter position (movement center) of the minute movement of the focuslens is greatly moved during the zooming to determine a following camtrack among many cam tracks, creating a possibility of defocusing (imageblur).

On the other hand, in this embodiment, the correction range is set, anda following cam track is determined among a small number of cam tracksrestricted within the correction range. Thus, the movement amount of thecenter position (center movement amount) of the focus lens in the minutemovement is small, enabling suppression of defocusing.

The small center movement amount of the focus lens provides an advantageof reducing a moving speed of the focus lens.

As shown in FIG. 9, inclination of the cam tracks is steeper on thetelephoto side than on the wide-angle side. Hence, when the focus lensis moved to trace the cam track, the moving speed of the focus lens atthe vertical synchronizing cycle increases as it moves toward thetelephoto side. When a large center movement in the infinite directionis added thereto, the moving speed of the focus lens further increases.The increase in moving speed of the focus lens causes noise or aperformance problem during driving of the focus lens.

On the other hand, restricting the correction range to reduce the centermovement amount enables mitigation of such a problem.

As a real operation in this embodiment, determination of the followingcam track by the minute movement of the focus lens is performed onlywithin the correction range between the upper limit 201 and the lowerlimit 202 shown in FIG. 2, and the center movement amount of the focuslens 105 is set so as not to exceed the correction range. This settingmethod is implemented at Steps S302 to S311 described below. As aresult, redetermination of the following cam track outside thecorrection range between the upper limit 201 and the lower limit 202 isinhibited.

Thus, in this embodiment, the correction range is set according to thedistance detection resolution of the object distance detection circuit127, and accurate determination of the following cam track is performedusing the AF evaluation values obtained only within the correctionrange. As a result, erroneous operations or defocusing caused by use ofthe AF evaluation values to redetermine the following cam track can besuppressed.

Referring back to FIG. 3, at Step S401, as in the case of Step S401 ofFIG. 4, the computer zoom unit 119 compares the AF evaluation values ofthe close side and the infinite side of the center cam track obtained bythe minute movement of the focus lens 105 with each other to determine adirection of the center movement.

At Step S402, the computer zoom unit 119 determines a necessity of thecenter movement based on the result of Step S401, and starts calculationof the center movement amount from step S302 if the center movement isnecessary. If the center movement needs to be performed, in other words,in an in-focus state, the computer zoom unit 119 proceeds to Step S405.

The calculation of the center movement amount implemented at Steps S302to S311 will be described below in detail.

Determination of the following cam track during zooming can beperformed, if the zooming is started from the wide-angle side, whilesuppressing defocusing more on the wide-angle side than on the telephotoside. A reason is as follows.

All the cam tracks are densely set on the wide angle side. Hence, evenwhen any of the cam tracks on the infinite side and the close side isselected as the following cam track, all the cam tracks can be coveredby a small center movement. Additionally, a depth of focus (distancerange where defocusing cannot be recognized by human eyes) is larger(deeper) on the wide-angle side, and thus the following cam track can bedetermined while suppressing defocusing.

However, an angle of view is wider on the wide-angle side, and hencevarious objects enter an AF target angle of view, and detection of adistance to a main object that is a focusing target object is difficult.As a result, there is a problem of a difficulty of determining thefollowing cam track.

On the telephoto side, the cam tracks are away from one another. Hence,in order to determine one following cam track from the plural camtracks, the center movement amount needs to be set larger than that onthe wide-angle side. However, due to a small depth of focus on thetelephoto side, the large center movement amount causes a difficulty ofdetermining the following cam track while suppressing defocusing. On theother hand, the angle of view on the telephoto side is narrower thanthat on the wide-angle side, and hence the distance to the main objectcan be easily obtained, which facilitates determination of the followingcam track.

In other words, the wide-angle side has characteristics that thedetermination of the following cam track is difficult while defocusinghardly occurs. The telephoto side has characteristics that thedetermination of the following cam track is easy while defocusing easilyoccurs.

For such characteristics, the depth of focus is an important factor. Thedepth of focus is determined based on the aperture diameter (apertureamount) of the aperture stop 103. When the aperture diameter of theaperture stop 103 is large, the depth of focus is small. In other words,defocusing easily Occurs. Conversely, when the aperture diameter issmall, the depth of focus is large, and defocusing is difficult tooccur.

Thus, in this embodiment, according to the aperture diameter (depth offocus) of the aperture stop 103, the center movement amount that is amovement amount of the movement center (center position) in the minutemovement of the focus lens 105 during zooming is changed, therebyfacilitating determination of the following cam track while suppressingdefocusing. The aperture diameter of the aperture stop 103 and the depthof focus are information on an operation or a state of the image takingoptical system.

FIG. 20 shows a relationship between the distance detection resolutionof the object distance detection circuit 127 and the correction range inthis embodiment. As described above, when the object distance obtainedby the object distance detection circuit 127 is 5 m, the correctionrange is restricted within the range of ±50 cm of the object distance.In other words, the upper limit 201 is equivalent to a cam track for anobject distance of 4.5 m, and the lower limit 202 is equivalent to a camtrack for an object distance of 5.5 m.

When the depth of focus is superimposed thereon, the range of the depthof focus is a range surrounded with an upper limit side curved line 221and a lower limit side curved line 222. For example, a wide-angle sidedepth of field (the depth of field is a value obtained by converting thedepth of focus into an object distance) is ±1 m around 5 m, a telephotoside depth of field is ±30 cm, which is smaller than the wide-angle sidedepth of field, and a range of the depth of field (that is, a range ofthe depth of focus) is smaller than the correction range.

As shown in FIG. 20, the correction range and the depth of focus have apoint P where a size relationship thereof is reversed at a certain focallength (zoom lens position). This point P changes depending on theobject distance and the aperture diameter. In a wide angle side rangewhere “depth of focus>correction range” is set with the point P as aboundary, the large depth of focus prevents defocusing from beingnoticeable during zooming.

The use of the object distance detection circuit 127 can solve theabove-described problem of presence of various objects in the AF targetangle of view on the wide angle side. The object distance detectioncircuit 127 detects object distances at one or several points in theangle of view irrespective of a size of the angle of view, and hence theobject distance detection circuit 127 can detect a distance to the mainobject even when the angle of view is wide.

In other words, in the wide-angle side range where “depth offocus>correction range” is set at the time of starting zooming, throughuse of the object distance detection circuit 127, a following cam trackpresent within the correction range is determined by the minute movementof the focus lens 105 and cam track changing by the center movement.This processing is important for zooming in which defocusing issuppressed.

Next, referring back to Step S302 of FIG. 3, setting of a centermovement amount W′ in this case will be described. The center movementamount W′ is determined based on a size relationship between the depthof focus and the correction range. The following cam track is presentwithin the correction range between the upper limit 201 and the lowerlimit 202, and hence even when any cam track present within thecorrection range is a following cam track during zooming, the centermovement amount W′ is set so as to determine the following cam trackduring zooming. Thus, the center movement amount W′ is set such that theminute movement can cover all the cam tracks from the infinite side tothe close side within the correction range.

At Step S302, the computer zoom unit 119 obtains the aperture diameter(aperture value) from the aperture stop 103. At Step S303, the computerzoom unit 119 calculates the depth of focus based on the aperture valueobtained at Step S302 and the zoom lens position.

At Step S304, the computer zoom unit 119 obtains a zooming speed Zsp andan exposure time period (shutter speed) of the image pickup element 106determined by the timing generator (TG) 132.

At Step S305, the computer zoom unit 119 determines the sizerelationship of the depth of focus and the correction range. When thecorrection range is smaller than the depth of focus (“correctionrange<depth of focus”), the computer zoom unit 119 proceeds to Step S306to calculates a zooming time period Tz (zooming time period in a rangewhere “depth of focus>correction range” is established) to the point Pwhere the depth of focus is equal to the correction range. The zoomingtime period can be calculated as follows:

Zooming time period Tx[s]=distance[pulse]÷zooming speed Zsp[pps] topoint P

At Step S307, the computer zoom unit 119 calculates a center movementfrequency M during the zooming time period Tz. The center movementfrequency M is proportional to the number of times of obtaining the AFevaluation values synchronized with the vertical synchronizing cycle V,and calculated by using the vertical synchronizing cycle V. In otherwords, the center movement frequency M can be calculated as follows:

Center moving frequency M=zooming time period Tz[s]×verticalsynchronizing cycle V[hz]

The center movement frequency M corresponds to the number of times ofobtaining the AF evaluation values.

Next, the computer zoom unit 119 calculates, by center movementsperformed M times during the zooming time period Tz, the center movementamount W′ that enables the minute movement of the focus lens 105 withinthe correction range from the lower limit 202 to the upper limit 201.This center movement amount W′ can be calculated by dividing thecorrection range by the center movement frequency M.

First at Step S308, the computer zoom unit 119 adds an error K to thecenter movement frequency M by taking some errors into consideration tocalculate the following C:

C=M−K (K is an integer of 1 or more)

The above calculation presumes an image pickup condition where theobject distance is not changed.

Next at Step S309, the computer zoom unit 119 calculates one centermovement amount W′ as follows:

Center moving amount W′=correction range/C

When the shutter speed is lower than the vertical synchronizing cycleV[hz], the center movement frequency M is calculated as follows:

Center moving frequency M=zooming time period Tz[s]÷shutter speed [s]

The center movement amount W′ may be changed according to the focallength (zoom lens position) in addition to the zooming speed and theshutter speed (exposure time period of the image pickup element 106).The zooming speed and the focal length are information on an operationor a state of the image taking optical system. The shutter speed isinformation on a photoelectric conversion operation of the opticalimage.

Next, referring to FIG. 20, a range where the depth of focus is smallerthan the correction range (“depth of focus<correction range”) on thetelephoto side from the point P will be described. Within this range,even within the correction range, only one erroneous center movement maycause defocusing. Thus, within this range, the center movement amount W′is set small to fine-correct the following cam track determined on thewide-angle side, thereby suppressing defocusing even when the erroneouscenter movement is performed. The center movement amount W′ accordinglyneeds to be set smaller than the depth of focus.

Referring back to Step S305 of FIG. 3, setting of the center movementamount W′ within this range will be described. At Step S305, thecomputer zoom unit 119 determines a relationship of “depth offocus<correction range”. Then, the processing proceeds to Step S310.

At Step S310, the computer zoom unit 119 calculates the center movementamount W′ as follows:

Center moving amount W′=correction range/C′

In the expression, C′ denotes a value that satisfies a relationship ofW′<depth of focus, and a value that is obtained by performing actualmeasurement by a sufficient number of times beforehand and where nodefocusing occurs until completion of zooming is used.

After completion of the processing, at Step S311, the computer zoom unit119 updates the minute movement position P_(x) as follows by adding thecenter movement amount W′ thereto:

Minute movement position P _(x) =P _(x) +W′

Next at Step S405, the computer zoom unit 119 calculates the cam trackparameters corresponding to the center cam track of the minute movement.This processing is similar to that of Step S405 shown in FIG. 4.Processing of Step S405 and subsequent steps thereof is similar to thatof FIG. 4.

As described above, in this exemplary embodiment, within the correctionrange (within moving range) for performing the minute movement of thefocus lens which is a range restricted based on the object distance, themovement amount of the center position in the minute movement is changedaccording to the aperture value (in other words, to the depth of focus).As a result, defocusing can be suppressed while improving determinationaccuracy of the following cam track by using the AF evaluation values.

Changing the center movement amount according to the zooming speed, thefocal length and the shutter speed enables further improvement of thedetermination accuracy of the following cam track.

Thus, according to this embodiment, the center movement amount ischanged according to at least one of information on the operation or thestate of the optical system and information on the photoelectricconversion operation of the optical image. Thus, completion of zoomingwithout determining any following cam track due to a reduction in numberof times of obtaining the AF evaluation values caused by the detectioncycle of the AF evaluation values during a fast zooming operation or aslow shutter operation, or due to the characteristics of the cam trackson the telephoto side can be prevented. Furthermore, zooming wheredefocusing caused by the minute movement of the focus lens fordetermining the following cam track is suppressed can be performed.

Furthermore, the present invention is not limited to these embodimentsand various variations and modifications may be made without departingfrom the scope of the present invention.

This application claims the benefit of Japanese Patent Application No.2009-005505, filed on Jan. 14, 2009, which is hereby incorporated byreference herein in its entirety.

1. A lens control apparatus configured to move a first lens unit forzooming and a second lens unit for focusing, the apparatus comprising: afocus signal generator configured to generate a focus signal indicatinga focus state of an optical system from a photoelectrical conversionsignal of an optical image formed by the optical system including thefirst and second lens units; a memory configured to store data generatedfor each predetermined in-focus distance and indicating a relationshipbetween a position of the first lens unit and a position of the secondlens unit; a controller configured to control, based on the data,movement of the second lens unit accompanying movement of the first lensunit; and a detector configured to detect information corresponding to adistance to a focusing target object, wherein the controller moves thesecond lens unit in an infinite direction and a close direction within amovable range set based on the information corresponding to thedistance, and wherein the controller changes a movement amount of acenter position of the movement of the second lens unit in the infiniteand close directions according to at least one selected from (a)information on an operation of the optical system, (b) information on astate of the optical system, and (c) information on a photoelectricconversion operation of the optical image.
 2. A lens control apparatusaccording to claim 1, wherein the optical system includes a light amountadjuster configured to adjust a light amount; and wherein the controllerchanges the movement amount of the center position according to anaperture size of the light amount adjuster, the aperture size being usedas the information on the state of the optical system.
 3. A lens controlapparatus according to claim 2, wherein the controller changes themovement amount of the center position according to a depth of focuscorresponding to the aperture size of the light amount adjuster.
 4. Alens control apparatus according to claim 1, wherein the controllerchanges the movement amount of the center position according to anexposure time period of an image pickup element configured tophotoelectrically convert the optical image formed by the opticalsystem, the exposure time period being used as the information on thephotoelectric conversion operation of the optical image.
 5. A lenscontrol apparatus according to claim 1, wherein the controller changesthe movement amount of the center position according to a moving speedof the first lens unit, the moving speed being used as the informationon the operation of the optical system.
 6. A lens control apparatusaccording to claim 1, wherein the controller changes the movement amountof the center position according to the position of the first lens unit,the position of the first lens unit being used as the information on oneof the operation and the state of the optical system.
 7. An opticalapparatus comprising: an optical system configured to include a firstlens unit for zooming and a second lens unit for focusing; and a lenscontrol apparatus configured to move the first lens unit and the secondlens unit, wherein the lens control apparatus comprising: a focus signalgenerator configured to generate a focus signal indicating a focus stateof the optical system from a photoelectrical conversion signal of anoptical image formed by the optical system; a memory configured to storedata generated for each predetermined in-focus distance and indicating arelationship between a position of the first lens unit and a position ofthe second lens unit; a controller configured to control, based on thedata, movement of the second lens unit accompanying movement of thefirst lens unit; and a detector configured to detect informationcorresponding to a distance to a focusing target object; and wherein thecontroller moves the second lens unit in an infinite direction and aclose direction within a movable range set based on the informationcorresponding to the distance, and wherein the controller changes amovement amount of a center position of the movement of the second lensunit in the infinite and close direction according to at least oneselected from (a) information on an operation of the optical system, (b)information on a state of the optical system, and (c) information on aphotoelectric conversion operation of the optical image.
 8. A lenscontrol method for moving a first lens unit for zooming and a secondlens unit for focusing, the method comprising: a focus signal generationstep of generating a focus signal indicating a focus state of an opticalsystem from a photoelectrical conversion signal of an optical imageformed by the optical system including the first and second lens units;a control step of controlling movement of the second lens unitaccompanying movement of the first lens unit based on data generated foreach predetermined in-focus distance and indicating a relationshipbetween a position of the first lens unit and a position of the secondlens unit; and a detection step of detecting information correspondingto a distance to a focusing target object, wherein the control stepmoves the second lens unit in an infinite direction and a closedirection within a movable range set based on the informationcorresponding to the distance, and wherein the control step changes amovement amount of a center position of the movement of the second lensunit in the infinite and close directions according to at least oneselected from (a) information on an operation of the optical system, (b)information on a state of the optical system, and (c) information on aphotoelectric conversion operation of the optical image.